A typical band saw machine of the type to which the invention pertains includes a tool carriage for supporting a saw blade which is driven about a pair of band wheels, and a support bed which supports a workpiece to be cut by the saw. The carriage is moveable toward and away from the support bed to advance the saw blade through the workpiece in a cutting operation and to withdraw the blade from the workpiece when the cutting operation is complete.
Monitoring systems for determining and displaying the feed rate of a band saw blade through a workpiece are known in the art. One such system employs at least two microswitches or limit switches which indicate the beginning and end of the cutting operation. One microswitch is located at a distance from the support bed which corresponds to the carriage position just prior to the point where the saw blade enters the workpiece. A second microswitch is located at the carriage position where the saw blade has cut through the work piece and contacts the support bed. An associated timing device measures the time duration of the cutting operation, and the system calculates the average feed rate of the blade through the workpiece based on the distance between the two switch locations and the measured time duration of the cutting operation.
This system presents a number of drawbacks. First, the system does not provide a real time indication of the feed rate of the saw blade throughout the workpiece. Rather, the operator must wait until the entire cutting operation is complete before the calculated feed rate can be obtained. Second, the system calculates only an average feed rate over the entire cutting operation. Thus, there is no indication of how the feed rate might vary during different portions of the cutting operation in the case, for example, where the workpiece does not present a consistent cross section. Further, the switch location indicating the start of the cutting operation must be continuously moved as workpieces having different profiles are cut by the band saw. This is the case since the distance between the support bed and the point where the saw blade initially engages the workpiece will likely change as the profiles of the workpieces change.
In an alternative system, a retractable wire spool is mounted on the tool carriage with the wire extending between the carriage and the support bed. The spool is linked to a quadrature encoder, and as the carriage moves toward the support bed during a cutting operation and the wire spool retracts, the encoder translates the movement of the carriage as displacement of the wire. Data signals representing the relative position of the carriage with respect to the workbed are fed to an associated rate meter which determines the feed rate of the saw blade through the workpiece based on the data provided by the encoder. The rate meter provides a visual display of the feed rate to a machine operator. This system does not record the feed rate, but simply displays the feed rate as the cutting operation proceeds. Thus, in order to determine the feed rate the operator must continuously observe the output of the rate meter throughout the actual cutting operation. The operator can adjust the operation of the machine based on the rate that is observed, but any adjustments are the result of completely manual feedback by the operator. No data is recorded and, therefore, no continuous real-time summary of the cutting operations performed by the band saw are provided. Thus, the operator cannot analyze the overall performance of the saw over a series of cutting operations to optimize productivity.
Accordingly, an improved band saw monitoring system would provide the following capabilities. The monitoring system would continuously calculate the relative position of the cutting blade with respect to the workpiece during the cutting operation and the direction of movement of the blade within, toward or away from the workpiece. Based on this data, the system would continuously determine the feed rate of the blade throughout the cutting operation. The system would also accurately determine the time duration of each cutting operation and provide an average feed rate for the entire cutting operation. The system would also determine the running speed of the cutting blade, i.e., the rate at which the saw blade is advanced around the band wheels. To optimize productivity and reduce premature blade failure, the system would provide a real-time display of the measured parameters to a machine operator for comparison with optimum values. The system would also preserve the measured data for future analysis.
It is, therefore, an object of the present invention to provide an improved machine monitoring system for a band saw which overcomes the above-described drawbacks and disadvantages of the prior art while providing the aforementioned capabilities.